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[experiment] test the cost of derive(Debug) code #164035

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[experiment] test the cost of derive(Debug) code #164035

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5caf311
try to remove all debug code to measure the cost of it
panstromek Oct 9, 2026
13085bd
avoid generating pointless matching
panstromek Oct 9, 2026
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2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/deriving/debug.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,7 @@ pub(crate) fn expand_deriving_debug(
safety: Safety::Default,
document: true,
};
trait_def.expand(cx, item, push)
trait_def.expand_ext_inner(cx, item, push, false, true)
}

fn formatter_ident(cx: &ExtCtxt<'_>, span: Span) -> Box<ast::Expr> {
Expand Down
13 changes: 13 additions & 0 deletions compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -460,11 +460,22 @@ impl<'a> TraitDef<'a> {
}

pub(crate) fn expand_ext(
self,
cx: &ExtCtxt<'_>,
item: &'a ast::Item,
push: &mut dyn FnMut(Box<ast::Item>),
from_scratch: bool
) {
self.expand_ext_inner(cx, item, push, from_scratch, false);
}

pub(crate) fn expand_ext_inner(
self,
cx: &ExtCtxt<'_>,
item: &'a ast::Item,
push: &mut dyn FnMut(Box<ast::Item>),
from_scratch: bool,
empty: bool
) {
let span = self.span;
let is_packed = matches!(
Expand Down Expand Up @@ -509,6 +520,8 @@ impl<'a> TraitDef<'a> {
let methods = self.methods.iter().filter_map(|method_def| {
let body = if from_scratch || method_def.is_static() {
method_def.call_substructure_method(cx, span, StaticEnum(enum_def), *ident)
} else if empty && enum_def.variants.len() > 0 {
method_def.call_substructure_method(cx, span, EnumDiscr(None), *ident)
} else {
method_def.expand_enum_method_body(cx, span, enum_def, *ident)
};
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_session/src/options.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2539,7 +2539,7 @@ options! {
flatten_format_args: bool = (true, parse_bool, [TRACKED],
"flatten nested format_args!() and literals into a simplified format_args!() call \
(default: yes)"),
fmt_debug: FmtDebug = (FmtDebug::Full, parse_fmt_debug, [TRACKED],
fmt_debug: FmtDebug = (FmtDebug::None, parse_fmt_debug, [TRACKED],
"how detailed `#[derive(Debug)]` should be. `full` prints types recursively, \
`shallow` prints only type names, `none` prints nothing and disables `{:?}`. (default: `full`)"),
force_intrinsic_fallback: bool = (false, parse_bool, [TRACKED],
Expand Down
78 changes: 15 additions & 63 deletions tests/ui/derives/deriving-all-codegen.stdout
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ impl ::core::marker::Copy for Empty { }
impl ::core::fmt::Debug for Empty {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::write_str(f, "Empty")
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -101,8 +101,7 @@ impl ::core::marker::Copy for Point { }
impl ::core::fmt::Debug for Point {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_struct_field2_finish(f, "Point", "x",
&self.x, "y", &&self.y)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -185,8 +184,7 @@ impl ::core::marker::Copy for PackedPoint { }
impl ::core::fmt::Debug for PackedPoint {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_struct_field2_finish(f, "PackedPoint",
"x", &{ self.x }, "y", &&{ self.y })
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -263,8 +261,7 @@ impl ::core::marker::Copy for TupleSingleField { }
impl ::core::fmt::Debug for TupleSingleField {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_tuple_field1_finish(f,
"TupleSingleField", &&self.0)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -338,8 +335,7 @@ impl ::core::marker::Copy for SingleField { }
impl ::core::fmt::Debug for SingleField {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_struct_field1_finish(f, "SingleField",
"foo", &&self.foo)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -422,13 +418,7 @@ impl ::core::marker::Copy for Big { }
impl ::core::fmt::Debug for Big {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
let names: &'static _ =
&["b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8"];
let values: &[&dyn ::core::fmt::Debug] =
&[&self.b1, &self.b2, &self.b3, &self.b4, &self.b5, &self.b6,
&self.b7, &&self.b8];
::core::fmt::Formatter::debug_struct_fields_finish(f, "Big", names,
values)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -672,8 +662,7 @@ struct Unsized([u32]);
impl ::core::fmt::Debug for Unsized {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_tuple_field1_finish(f, "Unsized",
&&self.0)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -751,8 +740,7 @@ impl<T: ::core::fmt::Debug + Trait, U: ::core::fmt::Debug> ::core::fmt::Debug
for Generic<T, U> where T::A: ::core::fmt::Debug {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_struct_field3_finish(f, "Generic", "t",
&self.t, "ta", &self.ta, "u", &&self.u)
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -871,8 +859,7 @@ impl<T: ::core::fmt::Debug + ::core::marker::Copy + Trait,
{
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::debug_tuple_field3_finish(f, "PackedGeneric",
&{ self.0 }, &{ self.1 }, &&{ self.2 })
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1037,11 +1024,7 @@ impl ::core::clone::Clone for Enum1 {
impl ::core::fmt::Debug for Enum1 {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match self {
Self::Single { x: __self_0 } =>
::core::fmt::Formatter::debug_struct_field1_finish(f,
"Single", "x", &__self_0),
}
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1109,7 +1092,7 @@ impl ::core::clone::Clone for Fieldless1 {
impl ::core::fmt::Debug for Fieldless1 {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::write_str(f, "A")
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1169,12 +1152,7 @@ impl ::core::marker::Copy for Fieldless { }
impl ::core::fmt::Debug for Fieldless {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
::core::fmt::Formatter::write_str(f,
match self {
Fieldless::A => "A",
Fieldless::B => "B",
Fieldless::C => "C",
})
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1250,16 +1228,7 @@ impl ::core::marker::Copy for Mixed { }
impl ::core::fmt::Debug for Mixed {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match self {
Self::P => ::core::fmt::Formatter::write_str(f, "P"),
Self::Q => ::core::fmt::Formatter::write_str(f, "Q"),
Self::R(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "R",
&__self_0),
Self::S { d1: __self_0, d2: __self_1 } =>
::core::fmt::Formatter::debug_struct_field2_finish(f, "S",
"d1", __self_0, "d2", &__self_1),
}
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1430,17 +1399,7 @@ impl ::core::clone::Clone for Fielded {
impl ::core::fmt::Debug for Fielded {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match self {
Self::X(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "X",
&__self_0),
Self::Y(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "Y",
&__self_0),
Self::Z(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "Z",
&__self_0),
}
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down Expand Up @@ -1536,14 +1495,7 @@ impl<T: ::core::fmt::Debug, U: ::core::fmt::Debug> ::core::fmt::Debug for
EnumGeneric<T, U> {
#[inline]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match self {
Self::One(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "One",
&__self_0),
Self::Two(__self_0) =>
::core::fmt::Formatter::debug_tuple_field1_finish(f, "Two",
&__self_0),
}
::core::result::Result::Ok(())
}
}
#[automatically_derived]
Expand Down
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